The Ireland star will miss the rest of this season’s domestic and international campaign after undergoing surgery in London yesterday on a toe injury.
Trimble, the Irish rugby writers’ Player of the Year in 2014, suffered a reoccurrence of the injury he sustained last October against Glasgow.
He is expected to be out of rugby until the summer but it is hoped he can recover ahead of pre-season and the Rugby World Cup.
Meanwhile, Ulster’s Craig Gilroy will become the youngster Ireland player to win 100 caps for his province when he plays against Treviso when the Pro12 resumes this evening (kick-off 7.35pm, live on BBC2 NI).
The 23-year-old wing is included in a side that shows five changes and two positional switches from their last big effort against Tigers last month.
Gilroy, who has scored 25 tries after touching down twice on his debut back in 2010, is selected on the right wing with Louis Ludik at full-back and Luke Marshall returning to the midfield alongside Darren Cave.
Ulster scrum-half Ruan Pienaarbelieves the province has the wherewithal to win the Pro12. After exiting the Champions Cup, it’s now all or nothing for Neil Doak’s men.
“Winning the Pro12 is obviously our focus and now it is definitely going to be in Belfast, it is a massive boost, ” said Pienaar.
ULSTER: L Ludik; C Gilroy, D Cave, L Marshall, M Allen, I Humphreys, R Pienaar; C Black, R Herring, W Herbst, L Stevenson, F Van der Merwe, R Wilson (Captain), M McComish, N Williams.
Replacements: J Andrew, A Warwick, B Ross, R Diack, C Ross, P Marshall, S McCloskey, P Nelson.